Mapping Regional Changes in Multiple-Timepoint Hyperpolarized Gas Ventilation Images and Validation by Radiologist Score.

Background: Hyperpolarized gas (HPG) magnetic resonance imaging, recently FDA-approved, offers an innovative approach to evaluating gas distribution and lung function in both adults and children. Purpose: In this study, we present an algorithm for calculating maps of changes in regional ventilation in asthma, cystic fibrosis, and COPD patients before and after receiving treatment. We validate the results with a radiologist's evaluation for accuracy. Our hypothesis is that the change map would be in congruence with a radiologist's visual examination. Assessment: Nine asthmatics, six cystic fibrosis patients, and five COPD patients underwent hyperpolarized 3He MRI. N4ITK bias correction, voxel smoothing, and normalization to the signal distribution's 95th percentile voxel signal value were performed on images. For calculating regional ventilation change maps, posttreatment images were registered to baseline images, and difference maps were created. Difference-map voxel values of > 60% of the baseline mean signal value were identified as improved, and those of < -60% were identified as worsened. In addition, short-term improvement (STI) was identified where voxels improved at Timepoint 2 but returned to baseline at Timepoint 3. A grading rubric was developed for radiologist scoring that had the following assessment categories: "level of volume discrepancy" and "discrepancy causes" for each ventilation change map. Results: In 15 out of the 20 cases (75% of the data), there was a small to no volume disparity between the change map and the radiologists' visual evaluation. The rest of the two cases had moderate volume differences, and three cases had large ones. Conclusion: Our regional change maps demonstrated congruence with visual examination and may be a useful tool for clinicians evaluating ventilation changes longitudinally.